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Show Syndrome of the Paramedian Thalamic Arteries: Clinical and Neuroimaging Correlation JOSE BILLER, M.D. JOHN J. SAND, M.D. JAMES J. CORBElT, M.D. HAROLD P. ADAMS, Jr., M.D. VAL DUNN, M.D. Abstract Two patients had sudden alteration of consciousness foUowed by fluctuating hypersomnia and bilateral ophthalmoplegia. Magnetic resonance imaging showed asymmetric, paramedian thalamic and midbrain lesions. The clinical and neuroimaging features are consistent with the syndrome of the paramedian thalamic arteries of the basilar communicating artery. These strokes were caused by an embolus to the rostral basilar artery originating from a fibrillating heart. Magnetic resonance imaging clearly delineates the delicate pattem of arterial involvement in mesodiencephalic junction infarctions. Introduction The clinical syndromes of infarctions at the mesencephalic-diencephalic junction are complex. l - ll Confirmation of these syndromes by arteriography or cranial computed tomography (CI) has been difficult because of the size of the involved vessels and the small lesions produced. Magnetic resonance imaging (MRI) permits excellent anatomical resolution of vascular lesions in the rostral brainstem and diencephalon. We report the cases of two patients in whom MRI studies corroborated the clinical findings of well-localized lesions in the thalamus and midbrain. The patients described here had asymmetric, paramedian thalamic and mesencephalic abnormalities attributed to rostral basilar artery embolism. From the Departments of Neurology and Radiology (VD), University o(Iowa College of Medicine, Iowa City. Iowa. Write for reprints to: Jose Biller, M.D., Department of Neurology, University of Iowa, Hospitals and Clinics, Iowa City, lA 52242. December 1985 Materials and Methods CT scans were performed on a Pieker International 1200 scanner using 5-mm-thick slices. CT scans were performed before MRI studies in both patients. The interval between CT and MRI was variable, but it was within a span of 96 h. MRI was performed with a 0.5-T supercondueling Picker Vista MR imaging system. Both T}"weighted and T2-weighted multislice images were obtained in the transverse plane in each case. TI-weighted images were performed with either (a) an inversion-recovery pulse sequence using an inversion time (T1) of 600 mls and a repetition time (TR) of 2,100 rnls, or (b) a spinecho pulse sequence using an echo time (TE) of 40 rnls and a TR of 550 rnls. T2-weighted images were performed with a spin-echo pulse sequence with aTE of 80 or 120 rnls and a TR of 2 s or greater. The criteria used to diagnose infarction were the presence of a focus of abnormally decreased signal intensity on T}"weighted images and a corresponding area of increased signal intensity on T2-weighted images. Case Reports Case 1 A 79-year-old woman was found unresponsive by family members. She had arterial hypertension and rheumatic heart disease with atrial fibrillation. On admission, she had a murmur of mitral stenosis accompanied by atrial fibrillation. She was somnolent and yawned frequently. Intermittently, she followed simple commands. She was able to swallow but had to be fed. There was bladder and rectal incontinence. There was bilateral, complete ophthalmoplegia. The left pupil was 5 mm and the right pupil was 4.5 mm; both were nonreactive. Cold-water calories produced no 217 Paramedian Thalamic Arteries Syndrome movements in either eye. She had a mild right hemiparesis. The electrocardiogram (ECC) revealed atrial fibrillation. M-mode and two-dimensional echocardiography showed mitral stenosis, aortic valvular calcification, left atrial enlargement, and moderate pericardial effusion. Cranial CT disclosed a hypodense area in the left thalamus consistent with a recent infarction (Fig. 1). MRI studies of the brain obtained within 24 h of the ictus revealed bilateral paramedian thalamic infarctions, more prominent on the left than on the right, and an asymmetric paramedian midbrain infarction (Fig. 2). The electroencephalogram (EEG) showed frequent, diffuse, biposterior dominant delta-theta slow waves consistent with bilateral, diffuse cerebral dysfunction. Because of the patient's history of rheumatic mitral stenosis and atrial fibrillation, she was treated with warfarin. The patient's hospital course was punctuated by a fluctuating mental status; at times she was quite alert, but most of the time she was somnolent. At her brightest, she was able to answer questions and whisper appropriately with few monosyllables. She had minimal improvement of her ophthalmoplegia, and by the time of her discharge, 2 weeks after admission, she was able to widen her right pal- Figure 1. Computed tomographic scan at the level of the thalamus demonstrates a subtle area of decreased density in the left thalamus (arrow). 218 pebraI fissure to 4 mm. Otherwise, her ophthalmoplegia was unchanged. Figun 2. Magnetic resonance image with T2-weighted spinecho technique (TE = 120 ms, TR = 2.9 s) indudes three contiguous slices through the thalamus and midbrain showing focal areas of abnormally high signal intensity compatible with infarction. In addition to the left thaJmUc ~esion .(top an:ow) there are bilateral paramedian thaWnk InfarctiOns (rruddle arrows). larger on the left, and a 1IIidbrain lesion that involves the paramedian region and extends asymmetrically to the left in its anterior extension (bottom arrow). Journal of Clinical Neuro-ophthaJmology C.se 2 A 61-year-old woman was found lethargic and dysarthric. She had a history of arterial hypertension, type II diabetes mellitus, atrial fibrillation, and a previous right occipitotemporal infarct with residual left homonymous hemianopsia. On admission, the patient's cardiac rate was irregular and she had an intermittent CheyneStokes respiratory pattern. She was arousable but slow to answer, with fluctuating hypersomnia. There was bladder incontinence. She was dysarthric and had a discrete right hemiparesis. There was a complete external ophthalmoplegia of the left eye. The right eye showed pathologic lid retraction, was deviated downward, and did not move volitionally or with vestibulo-ocular maneuvers above the midline. She was able to adduct the right eye minimally but sustained gaze poorly and had occasional downbeating movements. Both pupils were 3.5 mm and areflexic to light or accommodation (Fig. 3). Attempts at horizontal or vertical pursuit, saccades, or vestibulo-ocular reflexes (VOR) produced downbeating jerks of the right eye. After 4 days, brisk VOR mo~ements produced abduction of both eyes. Dunn~ the hyperpneic phase of Cheyne-Stokes respIration the lids were down, but during the apneic phase the right eye opened. ~ul?il size d~d not vary with Cheyne-Stokes respllation. Pupils failed to dilate after administration of 10% cocaine hydrochloride, but both dilated after 1% hydroxyamphetamine, indicating bilateral central sympathetic lesions. Routine blood studies yielded normal results except for a serum glucose level of 281 mg/dJ. The EeG demonstrated atrial fibrillation and left ventricular hypertrophy with st~ain. M-mo~e and two-dimensional echocardlOgraphy dISclosed calcified aortic stenosis. The EEG showed slowing of the background to 6 Hz, with frequently interspersed left-right shifting deltatheta. In addition, there was frontal intermittent rhythmic delta activity bilaterally. .,. cr showed an old right temporo-ocClpltal I~farct and a poorly defined hypodense area m the left thalamus and midbrain (Fig. 4). MRI studies of the brain obtained within 96 h of the ictus revealed asymmetric, paramedian thalamic and midbrain infarctions (Fig. 5). The patient was treated with heparin for 7 days and was then switched to warfarin. Two weeks after admission, her neurological condition was unchanged. Discussion The initial symptoms and signs of severe December 1185 Biller et al. somnolence and bilateral ophthalmoplegia in both patients suggested dysfunction of th~ rostral brainstem with nuclear and/or faSCIcular third nerve involvement and thalamosubthalamic structures. The second patient also had evidence of bilateral oculosympathetic dysfunction, suggesting that the first-order sympa,thetic fibers are paramedian in location, at least m the pretectum. The "pseudoabducens palsy" w~s probably due to bilateral supranuclear honzontal gaze paresis that rapidly cleared. 12 Adduction of the right eye was probably produced by convergence substitution. !'J'euroima~ing studies demonstrated asymmetrlc, paramedlan, thalamic, and midbrain lesions, probably the result of cardiogenic embolism to the rostral basilar artery. The syndrome of bilateral paramedian thalamic infarction is characterized by coma or hypersomnolence, gaze abnormalities, profound residual amnesia, and subcortical dementia.8- 11 The clinical, neuropsychological, and electrophysiological findings in patients with nonhemorrhagic thalamic infarction have been correlated with CT and postmortem findings. 13•I4 Segarra15 described changes in wakefulness as well as akinetic mutism in patients with mesencephalic lesions resulting from interruptio~ of reticulothalamic fibers as well as of ascending and des~ending tracts thattin the midbr~ to the limblc system. Caplan1 used the term top of the basilar" syndrome and provided an excellent' account of the many clinical presentations of this syndrome. The arterial blood supply to the human thal-amus is complex and subJ·ect to van.aii'ons17-23 (Fig. 6). The thalamoperforators also known as "paramedian thalamic" arteries supply the reticular, ventrolateral, medial, paraventricular, and centromedian nuclei of the thalamus.20 The paramedian thalamic arteries ~rise from the proximal segment of the postenor cerebral artery between the rostral end ~f the basilar. art~ry and the ostium of the posterior commurncating artery. The proximal segment of the posterior cerebral artery, also known as the "mesencephalic" artery,23 has been labeled the "basilar communicating" artery by Percheron.2o The basilar communicating artery gives off fanshaped thalamic art~ries an~ superior and ~nferior mesencephahc artenes. The supenor paramedian mesencephalic vess~ls, also ~own as paramedian peduncular artenes. of. FOlX and Hillemand,22 originating from the Ipsilateral or contralateral basilar communicating artery, supply the oculomotor r:\Uclear c~mpl~x and third nerve fibers traversmg the mtdbram, the anterior portion of the periaqueductal gray, the superior-medial portion of the red nucleus, the 219 Paramedian Thalamic Arteries Syndrome Figure 3. Top: Primary position at rest. Pathologic lid retraction and downward deviation (00) and complete extemal ophthalmoplegia (OS). Middle: Attempted right gaze; no movement was seen. Bottom: Slight adduction (DO) on attempted left gue. 220 Journal of Clinical Neuro-ophthalmoiosy BiUer et al. (b) ~ FJsure t. ComPU~!omographic scans at the le.vel o! the thalamus (iI) and midbrain (b) demonstrate poorly defined region of decreased densIty an the left thalamus and mldbram (arrows). and a large right oCcipital infarct. interpeduncular nucleus, and the superior cerebeUar peduncle decussation. 20 All of these vessels are end arteries, without meaningful anastomosis,17 and supply most of ~b) Yapre 5. Magnetic: retOnance images at the level of the thalamus (a) and midbrain (b) using T.·weighted inversion-recovery pu1Ie sequence (T. = 600 ms, TR = 2.1 s) demonstrate abnormal areas as dark regions, compared with normal. Image quality is somewhat degraded by patient motion. A large infarction is seen in the left paramedian thalamus (arrow) and a smaller abnormal area is seen on the right (small arrow). The midbrain infarction involves the midline and extends in a wedge shape ventrally and toward the left (large arrow). These abnormal areas were also seen on T2·weighted image. December 1985 221 Paramedian Thalamic Arteries Syndrome ACA 1. Polar A. 4. Post. lateral chor. A. 2. Paramedian A. 5. Thalamogenlculate 3. Post. medial chor. A. pedicle Figure 6. Vascular supply of the thalamus (modified from Castaigne et al.8). Polar A., polar artery; paramedian A., paramedian artery; post. medial chor. A., posterior medial choroidal artery; post. lateral chor. A., posterior lateral choroidal artery; ICA, internal carotid artery; ACA, anterior cerebral artery; MCA, middle cerebral artery; P Com A, posterior communicating artery; PCA. posterior cerebral artery; Bas Com A. basilar communicating artery; BA. basilar artery. the mesencephalic-diencephalic reticular activating substance. Several individual variations exist in the paramedian thalamic pedicle. 8 Often, there is a common origin of the paramedian thalamic and superior mesencephalic arteries from the basilar communicating artery; thus one basilar communicating artery may have a thalamo-mesencephalic territorial supply.zO This may have been the case in our patients having asymmetric paramedian thalamic and midbrain infarctions, although a large rostral basilar artery embolus could have occluded both arteries. Considering the structural anatomic and circulatory complexity of the thalamus, and the outstanding anatomical detail with increased sensitivity provided by MRI, we believe MRI is superior to CT in demonstrating the extent of disease. The thalamus and brainstem are best evaluated with transverse images using both T1and Tz-weighted pulse sequences. In general, TI-weighted images have better anatomic spatial resolution and Tz-weighted images may be more sensitive in detecting pathologic tissues. 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